Question: The scale on a map is 10cm : 1km. If two cities are 50cm apart on the map, what is the actual distance in km between the two cities?
Solution: The scale means that every 10cm on the map corresponds to an actual distance of 1km. A distance of 50cm on the map is the same as 5 $\cdot$ 10cm. The actual distance between the two cities is 5 $\cdot$ 1km, or 5km.